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Abstract

BACKGROUND

The Danish respiratory virus sentinel surveillance system has monitored influenza-like illness and influenza virus activity for over 30 years. During the last decade, additional virus groups were added. In 2021, the system was updated to include SARS-CoV-2, collect detailed symptomatic data, and transitioned to year-round surveillance.

AIM

To explore the first two seasons of year-round respiratory virus surveillance and the first symptomatic data collected in the Danish primary care sentinel surveillance system.

METHODS

In 2021/22 and 2022/23 seasons, 156 and 147 participating general practitioners, respectively, reported influenza-like illness consultation rates, collected symptomatic data and swabbed patient volunteers. Swabs were sent to Statens Serum Institut for multiplex PCR analysis, with additional characterisation using high-throughput sequencing or type-specific PCR assays for viruses such as influenza, SARS-CoV-2 and respiratory syncytial virus (RSV).

RESULTS

During the two seasons, 4,391 and 6,034 swabs, respectively, were collected and analysed. Year-round surveillance detected an unusually early wave of RSV during 2022/23. While present in nearly all weeks, SARS-CoV-2 showed waves with increased detection. Year-round surveillance also highlighted consistent patterns, such as continuous presence of entero-/rhinoviruses and endemic coronaviruses, as well as parainfluenza virus appearing after influenza virus. Symptom data showed differences by both sex and virus type, e.g. headaches were more commonly reported by women with RSV.

CONCLUSIONS

Our findings highlight the value of year-round respiratory virus surveillance in identifying both atypical virus activity and consistent patterns outside the winter season. Symptom data suggest the need for further research into sex-specific symptom patterns.

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This work is licensed under a Creative Commons Attribution 4.0 International License.
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2025-10-09
2025-11-11
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References

  1. Macias AE, McElhaney JE, Chaves SS, Nealon J, Nunes MC, Samson SI, et al. The disease burden of influenza beyond respiratory illness. Vaccine. 2021;39(Suppl 1):A6-14.  https://doi.org/10.1016/j.vaccine.2020.09.048  PMID: 33041103 
  2. Lyngse FP, Kirkeby C, Halasa T, Andreasen V, Skov RL, Møller FT, et al. Nationwide study on SARS-CoV-2 transmission within households from lockdown to reopening, Denmark, 27 February 2020 to 1 August 2020. Euro Surveill. 2022;27(6):1.  https://doi.org/10.2807/1560-7917.ES.2022.27.6.2001800  PMID: 35144726 
  3. Emborg HD, Carnahan A, Bragstad K, Trebbien R, Brytting M, Hungnes O, et al. Abrupt termination of the 2019/20 influenza season following preventive measures against COVID-19 in Denmark, Norway and Sweden. Euro Surveill. 2021;26(22):2001160.  https://doi.org/10.2807/1560-7917.ES.2021.26.22.2001160  PMID: 34085632 
  4. Adlhoch C, Sneiderman M, Martinuka O, Melidou A, Bundle N, Fielding J, et al. Spotlight influenza: The 2019/20 influenza season and the impact of COVID-19 on influenza surveillance in the WHO European Region. Vol. 26. Euro Surveill. 2021;26(40):1.  https://doi.org/10.2807/1560-7917.ES.2021.26.40.2100077 
  5. Chow EJ, Uyeki TM, Chu HY. The effects of the COVID-19 pandemic on community respiratory virus activity. Nat Rev Microbiol. 2023;21(3):195-210. PMID: 36253478 
  6. Bonacina F, Boëlle PY, Colizza V, Lopez O, Thomas M, Poletto C. Global patterns and drivers of influenza decline during the COVID-19 pandemic. Int J Infect Dis. 2023;128:132-9.  https://doi.org/10.1016/j.ijid.2022.12.042  PMID: 36608787 
  7. Mazick A, Christiansen AH, Samuelsson S, Mølbak K. Using sentinel surveillance to monitor effectiveness of influenza vaccine is feasible: a pilot study in Denmark. Euro Surveill. 2006;11(10):254-6.  https://doi.org/10.2807/esm.11.10.00654-en  PMID: 17130655 
  8. Larsen TG, Ginty JR, Jessen R, Nielsen RB, Jensen A, Botnen AB, et al. Virus Monitoring in Denmark: a community based self-sampling system to surveil respiratory viruses and associated symptoms. J Med Virol. 2025;97(4):e70293.  https://doi.org/10.1002/jmv.70293  PMID: 40130741 
  9. Statens Serum Institut (SSI). Overvågning af influenza, covid-19, RS-virus og andre luftvejssygdomme [Surveillance of influenza, COVID-19, RSV and other respiratory illnesses]. Copenhagen: SSI. [Accessed: 1 May 2025]. Available from: https://www.ssi.dk/sygdomme-beredskab-og-forskning/overvaagning-af-luftvejssygdomme
  10. European Centre for Disease Prevention and Control (ECDC). Operational considerations for respiratory virus surveillance in Europe. Stockholm: ECDC; 2022. Available from: https://www.ecdc.europa.eu/en/publications-data/operational-considerations-respiratory-virus-surveillance-europe
  11. Statens Serum Institut (SSI). EpiNews No 42/43 - 2023, Update on the whooping cough epidemic and vaccination of pregnant women / Respiratory infections in Denmark: Results from the extended sentinel surveillance in season 2021/22 and 2022/23. [Accessed: 3 May 2024]. Available from: https://en.ssi.dk/news/epi-news/2023/no-42-43---2023
  12. Praktiserende Lægers Organisation. PLO-læge- og praksispopulationen 1977 – 2022. Nøgletal fra medlemsregisteret. [Doctor and practice population 1977-2022. Key numbers from member registry]. Copenhagen: laeger.dk. [Accessed: 8 Sep 2025]. Available from: https://laeger.dk/media/3kkkkp1l/laege-_og_praksispopulationen_1977-2022.pdf
  13. Statens Serum Institut (SSI). Luftvejsinfektioner – overvågning. [Respiratory infections - surveillance]. Copenhagen: SSI. [Accessed: 1 May 2025]. Available from: https://www.ssi.dk/sygdomme-beredskab-og-forskning/sygdomsovervaagning/l/luftvejsinfektioner-overvaagning
  14. European Commission (EC). Commission Implementing Decision (EU) 2018/ 945 - of 22 June 2018 - on the communicable diseases and related special health issues to be covered by epidemiological surveillance as well as relevant case definitions. Official Journal of the European Union. Luxembourg: Publications Office of the European Union. 6.7.2018: L170. Available from: https://eur-lex.europa.eu/eli/dec_impl/2018/945/oj/eng
  15. Vega T, Lozano JE, Meerhoff T, Snacken R, Beauté J, Jorgensen P, et al. Influenza surveillance in Europe: comparing intensity levels calculated using the moving epidemic method. Influenza Other Respir Viruses. 2015;9(5):234-46.  https://doi.org/10.1111/irv.12330  PMID: 26031655 
  16. Corman VM, Landt O, Kaiser M, Molenkamp R, Meijer A, Chu DKW, et al. Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR. Euro Surveill. 2020;25(3):2000045.  https://doi.org/10.2807/1560-7917.ES.2020.25.3.2000045  PMID: 31992387 
  17. Dare RK, Fry AM, Chittaganpitch M, Sawanpanyalert P, Olsen SJ, Erdman DD. Human coronavirus infections in rural Thailand: a comprehensive study using real-time reverse-transcription polymerase chain reaction assays. J Infect Dis. 2007;196(9):1321-8.  https://doi.org/10.1086/521308  PMID: 17922396 
  18. Nielsen ACY, Böttiger B, Midgley SE, Nielsen LP. A novel enterovirus and parechovirus multiplex one-step real-time PCR-validation and clinical experience. J Virol Methods. 2013;193(2):359-63.  https://doi.org/10.1016/j.jviromet.2013.06.038  PMID: 23845901 
  19. Heim A, Ebnet C, Harste G, Pring-Åkerblom P. Rapid and quantitative detection of human adenovirus DNA by real-time PCR. J Med Virol. 2003;70(2):228-39.  https://doi.org/10.1002/jmv.10382  PMID: 12696109 
  20. Nagy A, Černíková L, Kunteová K, Dirbáková Z, Thomas SS, Slomka MJ, et al. A universal RT-qPCR assay for "One Health" detection of influenza A viruses. PLoS One. 2021;16(1):e0244669.  https://doi.org/10.1371/journal.pone.0244669  PMID: 33471840 
  21. World Health Organization (WHO). Manual for the laboratory diagnosis and virological surveillance of influenza. Geneva: WHO; 2011. Available from: https://www.who.int/publications/i/item/manual-for-the-laboratory-diagnosis-and-virological-surveillance-of-influenza
  22. Bagaria J, Jansen T, Marques DFP, Hooiveld M, McMenamin J, de Lusignan S, et al. Rapidly adapting primary care sentinel surveillance across seven countries in Europe for COVID-19 in the first half of 2020: strengths, challenges, and lessons learned. Euro Surveill. 2022;27(26):1-8.  https://doi.org/10.2807/1560-7917.ES.2022.27.26.2100864  PMID: 35775429 
  23. Lomholt FK, Emborg HD, Nørgaard SK, Nielsen J, Munkstrup C, Møller KL, et al. Resurgence of respiratory syncytial virus in the summer of 2021 in Denmark-a large out-of-season epidemic affecting older children. Open Forum Infect Dis. 2024;11(3):ofae069.  https://doi.org/10.1093/ofid/ofae069  PMID: 38495773 
  24. Morrow AL, Payne DC, Conrey SC, McMorrow M, McNeal MM, Niu L, et al. Endemic coronavirus infections are associated with strong homotypic immunity in a US cohort of children from birth to 4 years. J Pediatric Infect Dis Soc. 2024;13(5):265-73.  https://doi.org/10.1093/jpids/piae016  PMID: 38442245 
  25. (Norwegian Institure of Public Health (NIPH). Statusrapport for luftveisinfeksjoner Uke 14 (2025). [Statusreport for respiratory infections week 14 (2025)].Oslo: NIPH; 2025. Available from: https://www.fhi.no/contentassets/8a971e7b0a3c4a06bdbf381ab52e6157/statusrapport-for-luftveisinfeksjoner-_2025-14.pdf
  26. Hansen CH, Michlmayr D, Gubbels SM, Mølbak K, Ethelberg S. Assessment of protection against reinfection with SARS-CoV-2 among 4 million PCR-tested individuals in Denmark in 2020: a population-level observational study. Lancet. 2021;397(10280):1204-12.  https://doi.org/10.1016/S0140-6736(21)00575-4  PMID: 33743221 
  27. Fogh K, Graakjær Larsen T, Martel CJM, Trier Møller F, Skafte Vestergaard L, Trebbien R, et al. Surveillance of SARS-CoV-2 infection based on self-administered swabs, Denmark, May to July 2022: evaluation of a pilot study. Euro Surveill. 2023;28(38):1.  https://doi.org/10.2807/1560-7917.ES.2023.28.38.2200907  PMID: 37733236 
  28. Statens Serum Institut. Luftvejsinfektioner. [Respiratory infections]. Copenhagen: SSI. [Accessed: 31 Jan 2025]. Available from: https://experience.arcgis.com/experience/220fef27d07d438889d651cc2e00076c/page/Covid-19-Regionalt
  29. Sechan F, Edridge AWD, van Rijswijk J, Jebbink MF, Deijs M, Bakker M, et al. Influenza-like illness symptoms due to endemic human coronavirus reinfections are not influenced by the length of the interval separating reinfections. Microbiol Spectr. 2024;12(3):e0391223.  https://doi.org/10.1128/spectrum.03912-23  PMID: 38329364 
Primary care sentinel surveillance of influenza-like illness and laboratory detections of respiratory viral infections in Denmark, week 40 2021 to week 39 2023
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Amanda+Bolt+Botnen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Bolt Botnen Amanda</a>, <a href="/search?value1=Lisbet+Krause+Knudsen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Krause Knudsen Lisbet</a>, <a href="/search?value1=Julie+Grau&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Grau Julie</a>, <a href="/search?value1=Henrik+Bang&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Bang Henrik</a>, <a href="/search?value1=Jens+Nielsen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Nielsen Jens</a>, <a href="/search?value1=Jesper+Krog&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Krog Jesper</a>, <a href="/search?value1=Sofie+Midgley&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Midgley Sofie</a>, <a href="/search?value1=Kristina+Tr%C3%A6holt+Franck&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Træholt Franck Kristina</a>, <a href="/search?value1=Morten+Rasmussen&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Rasmussen Morten</a>, <a href="/search?value1=Uffe+Vest+Schneider&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Vest Schneider Uffe</a>, <a href="/search?value1=Hanne-Dorthe+Emborg&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Emborg Hanne-Dorthe</a>, <a href="/search?value1=Lasse+S+Vestergaard&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Vestergaard Lasse S</a>, <a href="/search?value1=Ramona+Trebbien&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Trebbien Ramona</a></span>. Primary care sentinel surveillance of influenza-like illness and laboratory detections of respiratory viral infections in Denmark, week 40 2021 to week 39 2023. <a href="/content/ecdc">Euro Surveill.</a> 2025;30(40):pii=2500103. <a href="https://doi.org/10.2807/1560-7917.ES.2025.30.40.2500103" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2025.30.40.2500103</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 07 Feb 2025;&nbsp;&nbsp; <span class="generated">Accepted</span>: 13 May 2025 </span> </p>
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